Abstract
A simple correlated valence fluctuation model is proposed as a possible mechanism for high-Tc superconductivity in certain copper oxides. Electron pairs are formed by Coulomb attraction between electrons in mainly Cu2+ (d9 configuration) pyramidal planes mediated by Cu3+ (d8 configuration) ions in the CuO4 chain-like plane in YBa2Cu3O7-x. These electron pairs have high binding energies necessary for high Tc, and the model is capable of explaining a number of other observed properties.